Improve write barriers in optimized code.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 7d590c29bc4a638d6fb49e0df4a9243faff84f3f..a8d4b7ccd458d2e26ec54ee5c40ff3f1a51d0d20 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -453,7 +453,8 @@ void MacroAssembler::RecordWriteField(
     LinkRegisterStatus lr_status,
     SaveFPRegsMode save_fp,
     RememberedSetAction remembered_set_action,
-    SmiCheck smi_check) {
+    SmiCheck smi_check,
+    PointersToHereCheck pointers_to_here_check_for_value) {
   // First, check if a write barrier is even needed. The tests below
   // catch stores of Smis.
   Label done;
@@ -482,7 +483,8 @@ void MacroAssembler::RecordWriteField(
               lr_status,
               save_fp,
               remembered_set_action,
-              OMIT_SMI_CHECK);
+              OMIT_SMI_CHECK,
+              pointers_to_here_check_for_value);
 
   bind(&done);
 
@@ -495,16 +497,88 @@ void MacroAssembler::RecordWriteField(
 }
 
 
+// Will clobber 4 registers: object, map, dst, ip.  The
+// register 'object' contains a heap object pointer.
+void MacroAssembler::RecordWriteForMap(Register object,
+                                       Register map,
+                                       Register dst,
+                                       LinkRegisterStatus lr_status,
+                                       SaveFPRegsMode fp_mode) {
+  if (emit_debug_code()) {
+    ldr(dst, FieldMemOperand(map, HeapObject::kMapOffset));
+    cmp(dst, Operand(isolate()->factory()->meta_map()));
+    Check(eq, kWrongAddressOrValuePassedToRecordWrite);
+  }
+
+  if (!FLAG_incremental_marking) {
+    return;
+  }
+
+  // Count number of write barriers in generated code.
+  isolate()->counters()->write_barriers_static()->Increment();
+  // TODO(mstarzinger): Dynamic counter missing.
+
+  if (emit_debug_code()) {
+    ldr(ip, FieldMemOperand(object, HeapObject::kMapOffset));
+    cmp(ip, map);
+    Check(eq, kWrongAddressOrValuePassedToRecordWrite);
+  }
+
+  Label done;
+
+  // A single check of the map's pages interesting flag suffices, since it is
+  // only set during incremental collection, and then it's also guaranteed that
+  // the from object's page's interesting flag is also set.  This optimization
+  // relies on the fact that maps can never be in new space.
+  CheckPageFlag(map,
+                map,  // Used as scratch.
+                MemoryChunk::kPointersToHereAreInterestingMask,
+                eq,
+                &done);
+
+  add(dst, object, Operand(HeapObject::kMapOffset - kHeapObjectTag));
+  if (emit_debug_code()) {
+    Label ok;
+    tst(dst, Operand((1 << kPointerSizeLog2) - 1));
+    b(eq, &ok);
+    stop("Unaligned cell in write barrier");
+    bind(&ok);
+  }
+
+  // Record the actual write.
+  if (lr_status == kLRHasNotBeenSaved) {
+    push(lr);
+  }
+  RecordWriteStub stub(isolate(), object, map, dst, OMIT_REMEMBERED_SET,
+                       fp_mode);
+  CallStub(&stub);
+  if (lr_status == kLRHasNotBeenSaved) {
+    pop(lr);
+  }
+
+  bind(&done);
+
+  // Clobber clobbered registers when running with the debug-code flag
+  // turned on to provoke errors.
+  if (emit_debug_code()) {
+    mov(dst, Operand(BitCast<int32_t>(kZapValue + 12)));
+    mov(map, Operand(BitCast<int32_t>(kZapValue + 16)));
+  }
+}
+
+
 // Will clobber 4 registers: object, address, scratch, ip.  The
 // register 'object' contains a heap object pointer.  The heap object
 // tag is shifted away.
-void MacroAssembler::RecordWrite(Register object,
-                                 Register address,
-                                 Register value,
-                                 LinkRegisterStatus lr_status,
-                                 SaveFPRegsMode fp_mode,
-                                 RememberedSetAction remembered_set_action,
-                                 SmiCheck smi_check) {
+void MacroAssembler::RecordWrite(
+    Register object,
+    Register address,
+    Register value,
+    LinkRegisterStatus lr_status,
+    SaveFPRegsMode fp_mode,
+    RememberedSetAction remembered_set_action,
+    SmiCheck smi_check,
+    PointersToHereCheck pointers_to_here_check_for_value) {
   ASSERT(!object.is(value));
   if (emit_debug_code()) {
     ldr(ip, MemOperand(address));
@@ -512,6 +586,11 @@ void MacroAssembler::RecordWrite(Register object,
     Check(eq, kWrongAddressOrValuePassedToRecordWrite);
   }
 
+  if (remembered_set_action == OMIT_REMEMBERED_SET &&
+      !FLAG_incremental_marking) {
+    return;
+  }
+
   // Count number of write barriers in generated code.
   isolate()->counters()->write_barriers_static()->Increment();
   // TODO(mstarzinger): Dynamic counter missing.
@@ -524,11 +603,13 @@ void MacroAssembler::RecordWrite(Register object,
     JumpIfSmi(value, &done);
   }
 
-  CheckPageFlag(value,
-                value,  // Used as scratch.
-                MemoryChunk::kPointersToHereAreInterestingMask,
-                eq,
-                &done);
+  if (pointers_to_here_check_for_value != kPointersToHereAreAlwaysInteresting) {
+    CheckPageFlag(value,
+                  value,  // Used as scratch.
+                  MemoryChunk::kPointersToHereAreInterestingMask,
+                  eq,
+                  &done);
+  }
   CheckPageFlag(object,
                 value,  // Used as scratch.
                 MemoryChunk::kPointersFromHereAreInterestingMask,